Declan Kidney acknowledged that his Ireland pack had been overpowered after the Springboks fought back from nine points down to win 16-12 in Dublin.
"Once South Africa got their mauling game going, they smothered us," said Kidney after his side failed to score in the second half of Saturday's game.
"With the breakdown, we were unable to get quick ball in the second half.
"We were going alright until half-time but Test matches always have four or five different parts."
The Ireland coach was without stalwarts like Brian O'Driscoll, Paul O'Connell and Rory Best at the Aviva Stadium but said he wouldn't make "excuses" for Ireland's defeat.
Props Michael Bent and David Kilcoyne and Ulster flanker Iain Henderson all came on to win their first caps as Ireland emptied their bench in the second half and Kidney said the experience would benefit the newcomers.
"We have a lot of young players and new caps that came into it today.
"It's all about being as positive as possible because we're just at the start of a (Autumn) series.
"We've got another big game against Fiji in Limerick next week and while there's a lot of inexperience, a lot of them stood up."
New Zealand-born Bent's parachuting into the Ireland squad having not even played a game for his new club Leinster came in for criticism from a number of ex-internationals but Kidney praised the prop's contribution after his 70th-minute introduction.
"We had conceded two penalties in the scrum previously. When he came on, he steadied it up and we managed to pick off a penalty."
South Africa's Ulster star Ruan Pienaar was relieved as his second-half try helped the Springboks regroup from a lacklustre opening 40 minutes.
"We had a terrible first half. Our kicking game wasn't that great. In the second half our forwards made a huge step up," said the scrum-half.
"We got a couple of good drives going, kept the ball and forced them to make errors.
"I'm very proud of the guys, especially in the second half."